class A1():
    arg = 30
    
class A(A1):
    arg_a = 10
    
class B():
    arg = 15

class C():
    arg = 20

class D(A,B,C):

    def test(self):
        print self.arg

#D -> A -> A1
#1. check D if exist  arg
#2. check A if exist  arg
#3. check A1 if exist arg

D().test()

